# UNDF: UNDF-2026-000001024
--- a/cmd/bisync/listing.go
+++ b/cmd/bisync/listing.go
@@ -727,8 +727,14 @@ func (b *bisyncRun) recheck(ctxRecheck context.Context, src, dst fs.Fs, srcList,
 	var srcObjs []fs.Object
 	var dstObjs []fs.Object
-	var resolved []string
 	var toRollback []string
+	resolvedSet := make(map[string]struct{})
+
+	// Build a map from dstObj.Remote() to dstObj for O(1) lookup
+	// instead of O(S*D) nested loop
+	dstByRemote := make(map[string]fs.Object)
+	dstByAlias := make(map[string]fs.Object)

 	if err := operations.ListFn(ctxRecheck, src, func(obj fs.Object) {
 		srcObjs = append(srcObjs, obj)
@@ -740,29 +746,33 @@ func (b *bisyncRun) recheck(ctxRecheck context.Context, src, dst fs.Fs, srcList,
 		fs.Debugf(dst, "error recchecking dst obj: %v", err)
 	}

+	for _, dstObj := range dstObjs {
+		dstByRemote[dstObj.Remote()] = dstObj
+		alias := b.aliases.Alias(dstObj.Remote())
+		if alias != dstObj.Remote() {
+			dstByAlias[alias] = dstObj
+		}
+	}
+
 	putObj := func(obj fs.Object, list *fileList) {
 		hashVal := ""
 		if !b.opt.IgnoreListingChecksum {
@@ -760,18 +770,20 @@ func (b *bisyncRun) recheck(ctxRecheck context.Context, src, dst fs.Fs, srcList,

 	for _, srcObj := range srcObjs {
 		fs.Debugf(srcObj, "rechecking")
-		for _, dstObj := range dstObjs {
-			if srcObj.Remote() == dstObj.Remote() || srcObj.Remote() == b.aliases.Alias(dstObj.Remote()) {
-				// note: unlike Equal(), WhichEqual() does not update the modtime in dest if sums match but modtimes don't.
-				if b.opt.DryRun || b.WhichEqual(ctxRecheck, srcObj, dstObj, src, dst) {
-					putObj(srcObj, srcList)
-					putObj(dstObj, dstList)
-					resolved = append(resolved, srcObj.Remote())
-				} else {
-					fs.Infof(srcObj, "files not equal on recheck: %v %v", srcObj, dstObj)
-				}
+		remote := srcObj.Remote()
+		dstObj, found := dstByRemote[remote]
+		if !found {
+			dstObj, found = dstByAlias[remote]
+		}
+		if found {
+			// note: unlike Equal(), WhichEqual() does not update the modtime in dest if sums match but modtimes don't.
+			if b.opt.DryRun || b.WhichEqual(ctxRecheck, srcObj, dstObj, src, dst) {
+				putObj(srcObj, srcList)
+				putObj(dstObj, dstList)
+				resolvedSet[remote] = struct{}{}
+			} else {
+				fs.Infof(srcObj, "files not equal on recheck: %v %v", srcObj, dstObj)
 			}
 		}
-		// if srcObj not resolved by now (either because no dstObj match or files not equal),
-		// roll it back to old version, so it gets retried next time.
-		// skip and error during --resync, as rollback is not possible
-		if !slices.Contains(resolved, srcObj.Remote()) && !b.opt.DryRun {
+		if _, ok := resolvedSet[remote]; !ok && !b.opt.DryRun {
 			if b.opt.Resync {
 				err := errors.New("no dstObj match or files not equal")
 				b.handleErr(srcObj, "Unable to rollback during --resync", err, true, false)